Here's a little trick I found when handling multiple nested models in a form that require validations for each model.
Spec time. For example, we have a model, Author, which has_many Books and has_many Magazines. Book and Magazine has validations. On a single page, we create a three forms for Book, Magazine, and Author. There is also an option select that a user can choose if the Author has a Book or a Magazine.
Pretty straight forward. Let's do some code.
#models/author.rb
class Author < ActiveRecord::Base
has_many :books
has_many :magazines
accepts_nested_attributes_for :books
accepts_nested_attributes_for :magazines
validates_presence_of :name
end
#models/book.rb
class Book < ActiveRecord::Base
belongs_to :author
validates_presence_of :title,
:genre
end
#models/magazine.rb
class Magazine < ActiveRecord::Base
belongs_to :author
validates_presence_of :title,
:genre
end
Basic model setup with validations and accepts_nested_attributes_for. More info on that can be found in the Ruby on Rails API - Nested Attributes.
Moving on to the form setup..
#views/authors/new.html.erb
<% form_for @author do |f| %>
<%= f.error_messages %>
<%= f.label :name %>
<%= f.text_field :name %>
<%= f.radio_button("media_type", "book" %><%= f.label :media_type_book, 'Book' %> [?]
<%= f.radio_button("media_type", "magazine" %><%= f.label :media_type_magazine, 'Magazine' %> [?]
<% f.fields_for :books do |book| %>
<%= book.label :title %>
<%= book.text_field :title %>
<%= book.label :genre %>
<%= book.text_field :genre %>
<% end %>
<% f.fields_for :magazines do |magazine| %>
<%= magazine.label :title %>
<%= magazine.text_field :title %>
<%= magazine.label :genre %>
<%= magazine.text_field :genre %>
<% end %>
<%= f.submit 'Submit' %>
<% end %>
That sets up the form with the nested model, now for the controller code.
#controllers/authors_controller.rb
class AuthorsController < ApplicationController
def new
@author = Author.new
books = @author.books.build #this builds the nested form in the view
magazines = @author.magazines.build #this builds the nested form in the view
end
def create
param_hash = params[:author]
if params[:author][:media_type] == "book"
param_hash.delete("books_attributes")
elsif params[:author][:media_type] == "magazine"
param_hash.delete("magazines_attributes")
end
@author = Author.new(param_hash)
@author.save
end
end
Instead of passing the params straight to Author.new, it's put into a hash variable. Then the params get checked for a title and genre, if empty delete the key from the hash and pass to Author.new. Activerecord wont see the book param and will skip the validations for it.
